Eurosceptic MPs are on manoeuvres with the formation of a cross-party group calling for an EU referendum.

The move comes after a respected think-tank warned now is not the moment for Britain to seek a renegotiation of its relationship with Europe, setting up the prospect of intense debate over the UK's response to the eurozone crisis at this year's party conferences.

Earlier this year 100 mostly Tory MPs proposed that the government legislate to require the next parliament to hold a referendum on Britain's continued membership of the European Union.

Now its organiser, Conservative backbencher John Baron, has secured sufficient support for the formation of an all-party parliamentary group on the issue, which will hold its inaugural meeting on October 16th.

The all-party group is not overtly eurosceptic as it is seeking to attract politicians who simply want to end calls for a referendum.

But it will place David Cameron under added pressure ahead of next month's Conservative party conference, where the party will endure its annual agonising over Britain's relationship with Brussels.

"There is a very real lack of public trust when people hear politicians making promises about Europe," Baron said.

"The three main political parties have failed in this respect. Such a referendum would address this credibility gap."

It is not yet clear how much support from outside the Tory party the group has attracted. Establishing all-party groups requires the support of 20 MPs in total. Ten must sit on the opposition benches, of which six must be from the main opposition party.

The group's formation came as a think-tank warned the eurozone crisis made reappraisals of the European Union's political makeup less likely - despite European Commission president Jose Manuel Barroso yesterday admitting his ultimate goal was the creation of a "federation of nation states".

John Chipman, the director-general and chief executive of the International Institute for Strategic Studies (IISS), said that "mutual diplomatic restraint" would be required to prevent the eurozone crisis turning into "a game of Russian routlette".

He explained: "The UK or others cannot use the crisis to renegotiate the parts of its EU membership it does not like, while Germany or others cannot try to use the crisis to squeeze non-eurozone countries into a political union they cannot accept."

Baron said that the IISS' view, expressed in its Strategy Survey 2012 published today, "gives the lie" to the British government's claims that they intend to repatriate powers.

He told politics.co.uk: "If this is not a good time to be discussing the issue, when the makeup and the very structures of the EU or eurozone are in a state of flux, when is a good time?"

The IISS fears that the delays and difficulties experienced in the negotiation of any EU constitution means steps to cope with the eurozone crisis will have to come before, rather than after, any serious attempt to reform the EU's political arrangements.

"Everybody who has in the past negotiated that EU constitutions knows this is not a process that is done overnight," Chipman told politics.co.uk.

However, he added: "The right moment to begin talking about what would be a new relationship with the European Union would be at a time when there is an actual negotiation of that in a formal sense within the EU itself. The time for that will not be short, but I don't think it's something that can be delayed for a matter of years either.

"While there is necessary and urgent crisis management activity around the question of the euro itself, the constitutional debate cannot be interminably delayed."

Alex Nicoll, Strategic Survey editor, suggested that if the eurozone does survive, the strategic implications of a stronger central role for Germany and a European tied more closely together both politically and economically would be hard to ignore.

"Britain has had a very ambivalent relationship with Europe for years now - I see that continuing," he said.

"Even Conservative prime ministers have reached compromises which they judge to be in the best interest of Britain."

Nicoll pointed out that David Cameron's veto of moves towards greater fiscal integration in December 2011's crunch summit had very little impact beyond pleasing his backbenches. "It didn't mean anything," he added.